Dralnu, Lich Lord, the general of an army of undead monstrosities hungry for brains. Mill your opponents' libraries by letting massive armies of undead munch their cards away. Tutor or transmute your way into finding Undead Alchemist, and then swarm with massive armies of undead while also casting powerful mill-spells like Traumatize, and then recurring them with Dralnu, to create even more massive armies of undead.
Tutoring - Since this deck is pretty combo-heavy, it has plenty of ways to tutor to find the correct pieces. "Standard" tutors include Diabolic Tutor, Demonic Collusion, Rhystic Tutor, and Long Term Plans. Rune-Scared Demon is a 6/6 flying demon and a tutor rolled into one (win win?). Since Undead Alchemist is the most important piece of this deck, there's a couple of transmute cards specifically for finding the alchemist (clutch the undercity, dimir house guard). Corpse Harvester can also be used to find Undead Alchemist, or any other zombie.
Milling Fun - Undead Alchemist is obviously the hero in the mill strategy, as he not only converts all damage you deal via zombies into milling, he also creates massive amounts of 2/2 zombies in the process, while also exiling their creatures so they won't ever come back. Combine with a Traumatize or Memory Sluice and all of a sudden you have a horde at your disposal. Geth, Lord of the Vault and Lichlord of Unx, great mill cards in their own right, work even greater when paired with the alchemist.
Hordes a-plenty - Rotlung Reanimator is definitely the most fun horde-maker. With Xenograft or an Artificial Evolution, he makes any zombie that dies produce a 2/2 zombie as a replacement. Together with sac engines like Gutless Ghoul, or Pestilence, and Vengeful Dead out, you can kill your opponents without even attacking. Endless Ranks of the Dead is an obvious choice for horde-creation, and Pestilence together with Nested Ghoul can produce frequent 2/2s for only a black mana a-piece. Another wonderful way to amass massive swarms of undead is the Rooftop Storm + Null Profusion combo, making all zombies freebies and allowing you to draw after casting each one. You can even cast your general for free (though, each time he dies it costs an additional 2 colorless, but really, that's still a steal for his ability. And if the sacrificing permanents is scary to you, just pay 1 B with pestilence and sacrifice him to himself, and just recast him whenever you need to recur something).